templater: add shorthand for building a dict like {"key": key} Like field init shorthand of Rust. This is convenient for building a JSON object from selected keywords. This means dict() won't support Python-like dict(iterable) syntax because it's ambiguous. Perhaps it could be implemented as 'mapdict(xs % (k, v))'.

templater: find keyword name more thoroughly on filtering error Before, it could spill an internal representation of compiled template such as [(<function runsymbol at 0x....>, 'extras'), ...]. Show less cryptic message if no symbol found. New findsymbolicname() function will be also used by dict() constructor.

templater: add dict() constructor It's troublesome to build JSON by template, so let's add programmatic way.

templatekw: add public function to wrap a dict by _hybrid object